Light scattering from extended kinetic models: polyatomic ideal gases

We propose an extended kinetic model for polyatomic ideal gases that replac es the Boltzmann collision operator with a single relaxation-time term. The model contains several position and time dependent coefficients that are d etermined by keeping some of the main properties of the Boltzmann descripti on for polyatomic gases of rough spherical molecules. As an application, we calculate the spectral distribution of light scattered by density fluctuat ions in polyatomic gases by solving the linearized kinetic model equation a s an initial value problem. Numerical results for the light scattering spec trum are derived for methane (CH4) and compared with the predictions of the extended hydrodynamic theory of Hammond and Wiggins which are in complete agreement with experimental data. (C) 1999 Elsevier Science B.V. All rights reserved.